Future demands on communication systems include increased component densities in the apparatus used and larger bandwidths. The data rates of computers, telecommunication, etc. are permanently increasing. Due to restriction in space and the high impedance characteristics of thin electrical lines, a higher component density on printed circuit boards, PCBs, results in difficulties in providing a sufficient number of electrical connections to a backplane, BP. Due to the large bandwidth and low signal loss that optical fibers exhibit, optical interconnections used for signal transmission internally on circuits boards and between boards may reduce these problems.
Thus, optical communication, well established since long times in long distance broad band communications, is also being introduced for short range applications inside telecommunication exchanges and computers, etc. For such applications the number of optical interconnections may become significant. However, a large number of loose optical fibers mounted on PCBs or BPs or connected thereto will give an unmanageable building practice. Optical fiber management is one of the key factors that have to be solved in order to successfully implement the use of short range optical interconnections. One practical approach thereto is to use a physically or geometrically separate optical level to house all the optical connections. A suitable such short range, separate optical interconnecting medium comprises optical fibers mounted on or in a flexible substrate called an optical fiber flexfoil.
The optical flexfoil technique has been presented by the company AT&T in e.g. U.S. Pat. No. 5,259,051 for Burack et al. This patent discloses how optical fibers are routed on an adhesive-coated surface using a rotating wheel. In addition the patent describes how optical fibers are encapsulated between two plastic foils, using two heated cylinders. AT&T's technique includes a thermoplastic filler which is added to the base flexfoil as an extra layer before the lamination in order to encapsulate and protect the fibers. The thermoplastic filler, which is molten by the two heated cylinders laminating a top foil to the thermoplastic layer, seals the fiber flexfoil. In order to melt the filler and in order to laminate the flexfoil without trapping air, high temperatures and high lamination pressures are required.